<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>class选择器</title>
    <style type=""text/css">
    .red{
       color:red;   /*红色 */
       font-size:18px; /*文字大小*/
    }
    .green{
       color:green;
       font-size:20px;
    }
    </style>
</head>
<body>
   <p class="red">class选择器1</p>
   <p class="green">class选择器2</p>
   <h3 class="green">class选择器3</h3>

</body>
</html>